I. Field of the Invention
The present invention relates to communications. More particularly, the present invention relates to a novel and improved communication system, wherein a user transmits variable-rate data on an allocated traffic channel, but when the user's variable transmission exceeds the capacity of the allocated traffic channel, the user is provided temporary use of an overflow channel to use with the allocated traffic channel in order to transmit the high-rate data.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband (ACSSB) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system are disclosed in U.S. Pat. No. 4,901,307, entitled, “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled, “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference.
The method and apparatus for the generation of a pseudorandom noise (PN) signal that is well suited for CDMA applications is disclosed in U.S. Pat. No. 5,228,054 issued Jul. 13, 1993, entitled, “POWER-OF-TWO LENGTH PSEUDO-NOISE SEQUENCE GENERATOR WITH FAST OFFSET ADJUSTMENT,” assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference.
CDMA by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Space or path diversity is obtained by providing multiple signal paths through simultaneous links from a mobile user through two or more cell-sites. Furthermore, path diversity may be obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Examples of path diversity are illustrated in copending U.S. Pat. No. 5,101,501, entitled, “SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM,” and copending U.S. Pat. No. 5,109,390, entitled, “DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee of the present invention and incorporated by reference herein.
An additional technique that may be used to increase the efficiency of the allocation of the communication resource is to allow the users of the resource to provide data at varying rates thereby using only the minimum amount of the communication resource to meet their service needs. An example of a variable rate data source is a variable rate vocoder, which is detailed in U.S. Pat. No. 5,414,796, issued May 9, 1995, entitled, “VARIABLE RATE VOCODER,” assigned to the assignee of the present invention and incorporated herein by reference. Since speech inherently contains periods of silence, i.e. pauses, the amount of data required to represent these periods can be reduced. Variable rate vocoding most effectively exploits this fact by reducing the data rate for these periods of silence.
In a variable rate vocoder of the type described in aforementioned U.S. Pat. No. 5,414,796, approximately 40% of the speech packets are coded at full rate. In the vocoder described in the patent application, the encoding rate is selected in accordance with the packet energy. When the packet energy exceeds a full rate threshold the speech is coded at full rate. In U.S. patent application Ser. No. 08/288,413, entitled, “IMPROVED METHOD AND APPARATUS FOR SELECTING AN ENCODING RATE IN A VARIABLE RATE VOCODER,” assigned to the assignee of the present invention and incorporated herein by reference, a method for determining based on characteristics of the speech packet if some of the packets to be coded at full rate can be coded at a lower rate without sacrificing perceived quality.
A variable rate speech encoder provides speech data at full rate when the talker is actively speaking, thus using the full capacity of the transmission packets. When a variable rate speech coder is providing speech data at a less that maximum rate, there is excess capacity in the transmission packets. A method for transmitting additional data in transmission packets of a fixed, predetermined size, wherein the source of the data for the data packets is providing the data at a variable rate is described in detail in copending U.S. Pat. No. 5,504,773, issued Apr. 2, 1996, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION,” assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference herein. In the above-mentioned patent application a method and apparatus is disclosed for combining data of differing types from different sources in a data packet for transmission.